This invention relates to a method for vulcanizing an elastomeric product using gas as a pressurizing medium.
In a conventional vulcanization method, an elastomeric product, such as a vehicular tire, is vulcanized by (1) placing the elastomeric product into a bladder containing mold (2) closing the mold while feeding shaping pressure into the bladder so as to bring the elastomeric product into contact with the inner surface of the mold by means of the inflated bladder; (3) supplying steam as a heating medium into the bladder after the mold is completely closed; (4) stopping the supply of steam either when the temperature of the elastomeric product rises to a predetermined level or when a predetermined time has elapsed; (5) supplying combustion gas or nitrogen gas as a pressurizing medium at a pressure equal to or higher than that of the steam; and (6) discharging the mixture of heating and pressuring mediums after a lapse of a predetermined time. In such vulcanization processes, the pipe inlets for supplying the pressurizing and heating mediums are open, while the outlet pipes for discharging the pressurizing and heating mediums are kept closed. In other words, the pipe outlets are dead ends. Also, only steam is used as the heating or bladder side medium to heat the elastomeric product from the inside. The gas is utilized for pressurization purposes.
If the elastomeric product is a large-size tire, a greater quantity of heat is necessary. This is because a large-size tire has a greater thickness than a smaller tire. Accordingly, a longer heating time is usually required for vulcanization of a large-size tire as compared to a smaller tire.
Normally the steam is supplied at a pressure of 13 to 15 kg/cm.sup.2, and the gas is supplied at a pressure of 18 to 28 kg/cm.sup.2. Accordingly, the steam pressure is lower than the gas pressure.
In the case of vulcanizing a large size tire, it is preferable from a tire quality viewpoint to change to the pressurizing process as soon as possible after starting the heating process. This is because of the trouble caused by air in the rubber or a resulting bareness produced in the cured tire. However, if the heating time is cut short, the to the tire is decreased and the vulcanization will have either a longer cure time as a result of making up for the thermal value shortage, or worse, will have under curing trouble.
It is an object of the present invention to provide a method for vulcanizing an elastomeric product which makes it possible to prevent air from being trapped in the elastomeric product and/or between the mold surface and the elastomeric product, or a bareness from occurring, and cure the elastomeric product without prolonging the cure time.